Internal combustion engine knock control system apparatus and method

ABSTRACT

A knock control system and method for operation of a spark ignition internal combustion engine having short-term regulation with a relatively large regulating action, such that when knocking events occur, the value for an actual ignition point is reset in the retard direction from a predetermined characteristic diagram value. In the absence of knocking events, the actual ignition point is advanced to the predetermined characteristic diagram value. Long-term adaptation is carried out such that the predetermined characteristic diagram value is reset from the knock limit by an adaptation value when knocking events occur during a change between a first operating condition to a second operating condition so that the short-term regulation is referred to a new predetermined ignition point value associated with the second operating condition. There is a switch-over to a smaller regulating action after an adaptation has been effected and after a minimum number of knockless ignitions have been desired. A more advanced ignition angle and improved efficiency of the internal combustion engine are achieved.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. Ser. No. 07/952,627 filedNov. 19, 1992, now abandoned the same inventors, which in turn is basedon PCT/EP92/00583 filed Mar. 18, 1992 and German application P4109432.8filed Mar. 22, 1991 for the same invention.

FIELD

The present invention relates to ignition control for an internalcombustion engine, and more specifically to a knock control system andmethod for a spark ignition internal combustion engine.

BACKGROUND

In order to achieve optimized operation in a spark ignition internalcombustion engine, it is necessary to vary the ignition timing orignition point in accordance with the engine speed and load. For thispurpose it is known practice to enter predetermined characteristicdiagram values (sometimes referred to as characteristic map input) in acharacteristic diagram (or characteristic map) of an electronic enginetiming device in accordance with the load and speed such that thecharacteristic diagram values can be read out for each actual ignitionpoint.

It is also known in the art to operate the internal combustion engine inthe higher load range close beneath the knock limit in order to optimizefuel efficiency and low pollutant emission levels. However, care must betaken to ensure that the knock limit is not exceeded, since the risk ofdamage to the engine is great if the knock limit is exceeded toofrequently. Since knock primarily occurs under wide-open-throttleoperating conditions, it is therefore a direct constraint on engineperformance. Further, since the position of the knock limit variesdepending upon existing engine operating parameters, in particular fuelgrade, temperature and air pressure, it is the known practice to controlor regulate knocking on a short-term basis.

In accordance with the short-term knock control practice describedabove, when knocking combustion or knocking events occur, thepredetermined characteristic diagram value taken from the characteristicdiagram is reset one step at a time by a control stroke in the directionof retarded ignition through a relatively large retard correction valueto a second adjusted diagram value for the actual ignition point. In thesubsequent absence of any further pinging or knocking events, theretarded value for the actual ignition point is advanced, one controlstroke at a time back to the original predetermined characteristicdiagram value.

This short-term control or regulation is therefore related to the levelof the predetermined characteristic diagram value entered in thecharacteristic diagram of the timing device for a particular engine.When the operating parameters are unfavorable, in particular when thefuel quality is poor, the knock limit may be relatively remote from thepredetermined characteristic diagram value or map input. In this case,the knock control must be carried out with stepwise control strokes ofan appropriate size and within a wide control band width. This has adisadvantageous effect on the control stability, since a relatively highnumber of knocking combustions, with sometimes violent and audibledetonations, must be tolerated during the knock control period. This hasan adverse effect on passenger comfort since knock produces unpleasantnoise due to the sometimes audible detonations. In addition, such aprotracted series of knocking combustions adversely affects the engineand the operation of the motor vehicle.

In the known practice, the short-term knock control starts with certaincontrol strokes upon reaching an operating point of a particular speedand load. Upon leaving this operating point and reaching anotheroperating point, the predetermined characteristic diagram value obtainedfrom the characteristic diagram usually also changes in correspondencewith the new operating point. The short-term control must then alsore-adapt to these new conditions. When the transition conditions areunfavorable, a reactively high number of knocking combustions withsometimes violent detonations must be tolerated until the short-termcontrol has re-adapted to the new operating point in the best possiblemanner.

Another problem with short-term knock control is that the first retardcorrection value has a fixed magnitude and cannot be automaticallyaltered to account for changing operational conditions. For example, inorder to stabilize out of knocking events as quickly and reliably aspossible, a relatively large regulating action with a relatively largeretard correction value is desirable. However, this is disadvantageousin that after subsequent knocking events, this technique causes theinternal combustion engine to operate well below the knock limit in aninferior operating range since a large retard adjustment of the ignitionangle has been made. It is therefore highly desirable to be able toreduce the magnitude of the correction value once such a large magnitudecorrection is no longer required.

It is also known practice to enter a plurality of set characteristicdiagrams and make them available as required. For example, a connectormay be installed in the engine compartment to switch from a specificcharacteristic diagram allocated to running on supergrade fuel to asecond preset characteristic diagram for use when running on regularfuel. Alternatively, a characteristic diagram switch-over may be carriedout automatically if a high number of knocking events is experienced.This automatic switch-over may be carried out by a learning functionassociated with a microprocessor or computer control means of the knockcontrol system. Examples of such learning systems are disclosed in U.S.Pat. No. 4,829,962 and published international patent application No.PCT/EP88/00523, now U.S. Pat. No. 5,076,235, the subject matter of whichare incorporated by reference as background for components of knockcontrol systems of the type described herein. However these switch-oversrepresent an overall change or resetting of the ignition point for theentire engine characteristic diagram. Also, as with the case above, anumber of knocking combustions must be tolerated during the switch-overperiod and the knock control range or band width is wide whentransitions are made thus giving an unfavorable effect on the controlstability.

Accordingly, there is a definite need in the art for an improved knockregulation system and method which overcomes the problems andshortcomings of the prior art.

THE INVENTION Objects

It is a primary object of the present invention to provide a knockcontrol method having short-term knock control for operation of theengine close beneath the knock limit for optimized engine performanceand having long-term adaption to quickly and reliably stabilize out ofknocking events once the knock limit is exceeded during a change from afirst operating condition to a second operating condition.

It is another object of the present invention to reduce the incidence ofknocking combustions and to keep knock control more stable overallduring the knock control period.

These and other objects of the present invention will become apparent tothose skilled in the art from the following detailed description of thepreferred embodiment, drawings and appended claims.

DRAWING

FIG. 1 is a basic block diagram of known internal combustion enginecontrol systems of the type having microprocessor ignition control towhich the present invention is applied;

FIG. 2 is a characteristic diagram of load Md versus ignition angleα_(z) which illustrates the position of the knock limit for variousengine load ranges; and

FIG. 3 is a diagram illustrating the adaptation of a reference levelα_(v) for the ignition angle α_(z) to a second reference level αL_(z)for short-term knock regulation through long-term adaptation and whereinthe operation with a large and a small regulating action is plotted.

SUMMARY

The present invention concerns a system and method for knock control ina spark ignition internal combustion engine comprising both long-termadaptation and short-term regulation techniques. The long-termadaptation is carried out such that a predetermined characteristicdiagram value entered in a characteristic diagram of an electronictiming device is adjusted away from the knock limit in the retarddirection by an adaptation value when knocking events occur, such thatthe short-term regulation is referred to a new ignition point inputvalue (predetermined characteristic diagram value plus adaptation value)or to a different level. The adaptation values are determined inaccordance with the occurrence of knocking events within certainrepetitive observation periods or monitoring intervals.

In this way, the reference level for control is redetermined within therepetitive observation periods and in accordance with the knockingevents occurring therein. During this time, the control range controlband width and hence the knock limit are maintained only a smalldistance from this reference level. The position of this reference levelis varied by adding suitable, determined correction values to the valuesfrom the entered characteristic diagram. This continuous repositioningof the reference level for the short-term control, together with thereduction in the control range, results in a reduction in the knockingcombustions and in violent detonations, thus improving comfort in termsof noise and reducing the load on the internal combustion engine. Inaddition, the overall knock control becomes more reliable and stable andthus easier to control.

In addition to varying the knock control reference level, the magnitudeof the regulating or controlling action is appropriately adjusted suchthat decreased magnitude retard and advance correction values are usedin place of the larger magnitude correction values associated with theknock control action of the previous operating point or condition. Thisswitch-over to smaller correction values is carried out when it can besafely assumed that a substantial regulating action is unnecessary, i.e.where the risk of engine knock occurring is generally not high and theinternal combustion engine is being operated in a lower load range wherethe risk of engine knock occurring is small. Favorable conditions ofthis kind exist and are detected according to the invention if a learnedadaptation value for the long-term adaptation is already present (forthe respective operating point) and a minimum number of knocklessignitions, one after the other, has been ascertained. In this way, itmay then be assumed that a subsequently occurring detonation is morelikely to be a random event such that a general and fast displacementregulation with a large retard adjustment and a large retard correctionvalue is unnecessary.

An observation period for determining the adaptation values or anevaluable dwell time at an operating point preferably amounts to atleast 500 ignitions. Owing to this type of switch-over to a smallerregulating action with smaller correction values, a more advancedignition angle may be maintained thus resulting in an overallimprovement in the efficiency of the internal combustion engine, sinceit may be consistently operated closer to the knock limit.

In accordance with a preferred embodiment of the invention, thepredetermined characteristic diagram values associated with a number ofadjacent engine operating points or conditions in the characteristicdiagram, corresponding to various speed and load ranges are combined ina manner which is known per se. For example, each cylinder of theinternal combustion engine may be allocated its own characteristicdiagram with a desired set of adaptation values for operation in acylinder-selective manner. Thus, each of the cylinders may be operatedseparately in a thermodynamically optimum manner, thereby making itpossible to keep fuel consumption and pollutant emissions to a minimum.In this way, it is convenient to enter adaptation values in correctioncharacteristic diagram areas associated with the characteristic diagramareas. These characteristic diagrams may, for example, be formed as an8×8 matrix with 8 defined speed points and 8 defined load points.

The long-term adaptation is carried out such that an adaptation valuecorresponding to the distance of the actual ignition point from thepredetermined characteristic diagram value is determined for aparticular operating condition or corresponding to a particular speedand load. This adaptation value is entered in a correctioncharacteristic diagram upon leaving the operating point and is output asa "learned" correction magnitude when this operating point is reached orexceeded again. Known learning algorithms may be used for this purpose.The predetermined characteristic diagram value is then acted upon bythis information for the anticipatory control of the short-termregulation.

The knock control thus comprises a kind of automatic learning processwherein, in addition to the predetermined characteristic diagram valueswhich are entered at the outset, adaptation values which depend fromcertain operating parameters are determined and stored during transitionto each new operating condition (point). An adaptation value of thiskind may, for example, be the value for retarding the ignition point ifthe vehicle had just been filed with fuel of an inferior quality. Inthis case the adaptation value is determined on the basis of theshort-term control such that it corresponds to the distance of the knocklimit from the predetermined characteristic diagram value, i.e., theadaption value corresponds approximately to the distance of the actualignition point away from the predetermined characteristic diagram value.If after leaving this operating point it is soon reached again, thelong-term conditions, such as the fuel quality in the fuel tank, willnot usually have undergone an abrupt and fundamental change. Thus, whenthe operating point is reached again, the predetermined characteristicdiagram value is acted upon by the stored adaption value, so that theregulation is controlled in an anticipatory manner and is started in thevicinity of the knock limit. In the absence of the anticipatory control,each time a new operating point is reached the regulation would usuallystart in a knocking range corresponding to the predeterminedcharacteristic diagram value, thus resulting in an undesirable number ofviolent detonations when stabilizing out of this range.

In one embodiment of the invention, an actual control stroke, preferablythe last control stroke before the respective operating point is left,is detected and stored as the adaptation value.

To provide better information on the position of the knock limit a morefavorable adaptation value may be obtained by averaging the controlstrokes. This averaging step is preferably carried out within a certainobservation time period, such as, for example, the dwell time at theignition point. In another embodiment, the control strokes present whena knocking event occurs are used for the averaging step. The averagingstep may be carried out over all control strokes within an observationperiod or during the dwell time at a certain ignition point. Both formsof averaging produce suitable, utilizable information regarding theposition of the knock limit and thus a suitable adaptation value.

As is well understood in the art, the knock limit is not a preciselydefined limit, but is rather seen as a statistical limit, such that itis possible for knocking events to occur above or below the determinedstatistical knock limit, depending upon the quality of the combustion atthe time. Therefore, since the position of the knock limit does not inany case represent a precisely defined magnitude, it has been founddesirable to enter an adaptation value in the correction diagram orreplace an old adaptation value by a new one only if the value of thechange in the averaged control strokes lies above the value of anestablished threshold. As the averaging of the control strokes onlyproduces utilizable results within a certain dwell time, it has alsobeen found advantageous to store adaptation values only when the numberof ignitions does not fall below a certain value.

The measures so far described enable the short-term control through theadaptation values to be moved from the entered predeterminedcharacteristic diagram value in the direction of retarded ignition. Ifthe knock limit gradually moves towards the original predeterminedcharacteristic diagram value again, for example, as a result ofrefilling with fuel of a better quality, the adaptation values which areentered for each operating point should also be re-adapted and broughtinto line again. This may be achieved by resetting the adaptation valueat a certain operating point in incremental steps of a certain returnmagnitude in the direction of the original predetermined characteristicdiagram value when no or only a few knocking events are detected.

According to the invention, a change-over from a large regulating actionto a smaller regulating action having smaller retard correction valueswill occur if there exists a learned long-time adaptation value for therespective operating point and where a knocking event has not beendetected during a certain time period or during a corresponding numberof ignitions. If there are considerable changes in the operatingconditions, however, there will be a switch-over to the knock regulatingalgorithm having the large regulating action with the correspondinglarge retard correction values. This switch-over to the knock-regulatingalgorithm takes place when knocking events occur during the stepwisereturn through the advance correction values in the short-term controlalgorithm or while the correction is being performed. It may then beassumed that, by altering the operating parameters, there is arelatively high risk for knock to occur, thus necessitating asubstantial regulating action. If the ignition correction is affectedwith a relatively small retard correction value, the ignition correctionis performed via advance correction values which are smaller than whenthe ignition correction is performed via greater retard correctionvalues. When a knocking event is identified, a counter may be set in asimple circuit in order to ascertain whether the knocking event occursagain during a switch-over condition until the correction has beencompletely worked through.

It is a further advantage of the invention to retain the currentadaptation value even when the internal combustion engine or the vehicleis stopped, so that the adaptation magnitude is immediately availableupon restarting the engine. As a result, the knock regulation operatesimmediately with the desired small regulation range.

DETAILED DESCRIPTION OF THE BEST MODE

The following detailed description illustrates the invention by way ofexample, not by way of limitation of the principles of the invention.This description will clearly enable one skilled in the art to make anduse the invention, and describes several embodiments, adaptations,variations, alternatives and uses of the invention, including what wepresently believe is the best mode of carrying out the invention.

Referring to FIG. 1, a conventional, known engine control system 20 ofthe type described above includes a basic set of performancecharacteristics assembled and stored in a memory unit 21, such as aread-only memory (ROM), which characteristics indicate ignition times ofa particular engine type as a function of load and speed. This basic setof performance characteristics is typically determined on a test-stand,by reference to several examples of the engine, and serves as thestarting point in controlling the engine in each vehicle having thatcorresponding type of engine. The speed n_(M) and the load M_(d)(torque) are now determined from suitable sensors (not shown) on theengine 26, and these characteristic operating parameters, which indicatea certain operating condition of the engine 26, are supplied to thecentral processing unit 24 where they are converted into memoryaddresses. On operating the engine 26 for the first time, the ignitiontime associated with a certain speed value and a certain load value isread out of the memory unit 21 on the basis of the address received fromthe central processing unit 24 and this value from the basic set ofperformance characteristics is transferred to the CPU 24 via theoperating data control circuit (abbreviated CCT in FIG. 1) 23.

Referring to all three Figures at the same time, the engine 26 ismonitored for detonating combustion (knocks), with the aid of a knocksensor (not shown). If a knock event is detected, a signal from thesensor will be fed to the operating data control circuit 23 whendetonating combustion occurs, via knock-signal condition unit 27 and aknock regulator 28. When a knock event is detected at the motor 26, thisknock signal K and the engine crankshaft-angle signal α_(z) will besupplied through the knock signal conditioning circuit 27, which isbasically a pulse shaper, to a multiplexer in the knock regulator 28. Ifa knock signal of this kind is received in association with a certainspeed value and a certain load value, a correction value (adaptationvalue) will be determined in the operating data control circuit 23 basedon the value in the basic set of performance characteristics(predetermined characteristic diagram value in ROM 21). This correctionvalue SK (see FIG. 3), will adjust the timing signal d_(z) beneath theknock limit by an amount R_(h) for this characteristic operatingparameter. This correction value is now stored in the correction datamemory 22 and becomes the original retard correction value SK₁.

If no knock signal results when a characteristic operating parameter (acertain speed and a certain load) occurs for the first time, the centralprocessing until will shift the ignition time α_(z) towards the knocklimit for this operating parameter, this being done in a stepwisemanner, RK₁, whenever this characteristic operating parameter occursuntil a knock signal is detected for the first time. The ignition-timevalue associated with this knock signal is then retarded by apredetermined correction value amount so that the ignition timing angleα_(z) lies slightly beneath the knock limit, and a correspondingcharacteristic diagram value α_(v) is stored in the set of data inmemory unit 22.

The ignition-time values, derived initially from the basic set ofperformance characteristics and then adjusted on the basis of this setof correction data, are subjected to a final correction by the centralprocessing unit 24, with respect to various furtherinfluence-parameters. These influence-parameters can be the airtemperature T_(L), the engine temperature T_(M), the atmospherichumidity φ_(L), and the fuel/air ratio λ, and the fuel type since theseparameters likewise influence fuel consumption-optimized operation. Thisforms the map of predetermined characteristic diagram values, α_(v).After applying the final correction, the ignition advance-and-retarddevice 25 is activated by control from the central processing unit 24,which then ensures that the engine 26 operates with optimum ignitiontimes.

The operation of the system of FIG. 1 will be described in conjunctionwith FIGS. 2 and 3, which illustrate in greater detail thecharacteristic diagram values and the retards applied to engine 26 viacontrol circuit 23. The engine speed n_(M) and load (engine torque)M_(d) are supplied from the engine 26 to the central processing unit 24as shown. The central processing unit 24 determines from theseparameters the address of the storage locations in the memory units 21and 22 which correspond to this characteristic diagram value. Thisaddress is simultaneously applied to the memories 21 and 22 to read outthe respective ignition-time value and retard value SK₁ stored at thesememory locations. The central processing unit 24 therefore applies afinal ignition-time signal to the ignition advance and retard device 25for control of the motor operation. Thus, the system is capable ofautomatically correcting the ignition-time values stored in the memoryunit 21 on the basis of the correction values stored in memory unit 22,these correction values being constantly changed and updated asdescribed in more detail below with respect to FIGS. 2 and 3 as knocksignals are generated during operation of the engine. In addition, thecentral processing unit 24 is capable of periodically adjusting thecorrection values in the memory unit 22 for those characteristicoperating parameters which are below the knock level to ensure that anoptimum control of the ignition timing at a level just below the knocklevel is maintained at all times.

FIG. 2 illustrates the dependency of the torque M_(d) on the ignitiontiming α_(z) for three engine load conditions indicated as load curves1, 4 and 6. The curve 1 represents a low engine load condition and isrelatively flat. The knock limit is indicated at 2 and lies a long wayfrom the maximum or peak 3 of the curve 1. For optimum performance, theinternal combustion engine is preferably operated at the peak of itsload curve or in this case at maximum or point 3. Thus, for a low-loadcurve such as curve 1, there is no danger that knocking combustions willoccur.

The curve 4 represents a half-load range and is curved to a greaterextent. In this case, the knock limit indicated at 2 has moved closer tothe maximum or peak point 5, i.e., the point of optimum operation of theinternal combustion engine. However, given an appropriate control, thereis also no risk of any knocking combustions here either.

The curve 6 represents the full-load range (full-open throttlecondition) where the knock limit 2 lies to the left or before the peak11. The risk of knock occurring is greatest in the area between thecurves 4 and 6 during optimized operation. This corresponds to the areawhere knock control is active. For the full-load range of curve 6, theoptimum operating point is at 7, which in this case, lies just beforethe knock limit 2. The double arrow 8 indicates the seeking movement ofthe predetermined ignition point value towards this point 7 by means ofthe short-term control.

FIG. 3 is a diagram which shows a plot of the value of the ignitionangle α_(z) (vertical axis) versus time (horizontal axis). The upperabscissa corresponds to a predetermined characteristic diagram valueα_(v) for the ignition angle point from an entered characteristicdiagram at a certain operating point. This predetermined characteristicdiagram value α_(v) is preferably selected so that the internalcombustion engine is operated close to the knock limit under normaloperating conditions. In this case knocking events may occur. This stateis illustrated as time period a in FIG. 3.

In accordance with known short-term regulation techniques, thepredetermined characteristic diagram value α_(v) is modified or reset instepwise fashion by a first large correction value SK₁ in the "retard"direction (often referred to as a regulation or control stroke) for anactual ignition point when knocking events, k, occur. When knockingstops, the value for the actual ignition point is advanced by stepwiseadvanced correction value RK₁, upon each ignition until it reaches thepredetermined characteristic diagram value α_(v).

Time period b represents a situation where the operating parametersundergo change of the operating condition, such as, for example afterrefuelling, where a lower quality fuel is permitted to mix with a fuelof a higher quality. In period b, an increased number of knocking eventsk will occur one after the other. In practice, for this situation, theactual ignition points are moved one after another further away from theoriginal predetermined characteristic diagram value αL_(z), at a(vertical) distance L_(z) from the predetermined characteristic diagramvalue α_(v). This is indicated diagrammatically by the arrow 9. The newlevel αL_(z) corresponds to a changed knock limit. The value L_(z)corresponds to a value (reduced by a predetermined small threshold)which is determined by averaging the previous control strokes R_(h) inan observation period t_(B).

Upon leaving the operating point for which the track of the ignitionpoint is illustrated in FIG. 3, the value L_(z) is stored in the knockcontrol system memory (not shown) as an adaptation value and isimmediately output again each time the operating point is reached, sothat the control immediately continues without any transient processesfor this operating point.

The track of the short-term control with a relatively large regulatingaction through relatively large retard correction values SK₁ and advancecorrection values RK₁ is illustrated in the time periods a, b, c. Inperiods a, b, and c, the large retard correction values SK₁ areindicated by the vertical displacements while the smaller advancecorrection values RK₁ are indicated by the upward inclineddisplacements. The long-term adaptation has already been assumed andbecomes active in the period c. The adaption value L_(z), is determinedby averaging the previous control in the observation period t_(B). Theshort-term control is therefore no longer related to the predeterminedcharacteristic diagram value α_(v), but rather to the newly determinedlevel αL_(z), which has been reduced by the adaptation value L_(z), sothat there is now also a re-control to this long-term level αL_(z). Thelong-term level αL_(z) is only altered relatively slowly.

The adaptation value L_(z) for the short-term control has thereforealready been assumed in the time period c and no more knocking eventshave been ascertained in the subsequent time period d (a certain minimumnumber of ignitions, preferably 500 being required for the time periodd). When these conditions occur there is a switch-over to a smallerregulating action having correspondingly smaller retard correctionvalues SK₂ and smaller return values as advance values RK₂.

This case is illustrated for the detonation K occurring at the beginningof time period e where the ignition angle is reset in the retarddirection by the reduced magnitude retard value SK₂ and return byreduced magnitude advance correction value RK₂. If no further knockingevents occur during the return (advance), the short-term control remainsswitched to the smaller magnitude correction values. However, should asubsequent knocking event K occur during a monitored return interval (inthe present case indicated as time period t_(R) at the end of the periode), there will be a switch-over to the values SK₁ and RK₁, for thegreater regulating action, as illustrated in the period f.

A graduated regulating action is thus carried out which on averageresults in more advanced ignition points and thus the efficiency of theinternal combustion engine operation is improved.

It should be understood that various modifications within the scope ofthis invention can be made by one of ordinary skill in art withoutdeparting from the spirit thereof. We therefore wish our invention to bedefined by the scope of the appended claims as broadly as the prior artwill permit, and in view of the specification if need be.

We claim:
 1. A knock control system apparatus for a spark ignitioninternal combustion engine operable under a plurality of operatingconditions comprising:a) first knock sensor means for producing signalsindicative of the occurrence of a knock, K, mounted in association withat least one cylinder of the engine, said knock signal being provided toa microprocessor; b) second sensor means for producing input signalsindicative of an ignition angle, α_(z), of said cylinder of the engine,said ignition angle input signal being provided to said microprocessor;c) means for advancing or retarding an ignition angle signal whichproduces a signal representative of an advance or retard of saidignition angle, α_(z) ; d) means for producing an ignition in saidcylinder in response to said advance/retard ignition angle signalproduced by said advance/retard signal producing means; e) amicroprocessor, having at least one memory means for storing andoutputting a signal corresponding to a predetermined characteristicdiagram reference level value, α_(v), from a base diagram stored inmemory, said diagram having a plurality of characteristic performancevalues, which characteristic diagram reference level value, α_(v),corresponds to a first reference level for an ignition point of theengine at a first operating condition having a first knock limit; f)said means for advancing or retarding said ignition controlling a knock,K, on a short-term basis during said first operating condition inresponse to a signal from said microprocessor corresponding to saidpredetermined characteristic diagram reference level value α_(v), ofsaid first reference level for the ignition point at said firstoperating condition, by resetting, in response to said knock signalprovided to said microprocessor when said knock, K, occurs, saidignition angle α_(z) in a retard direction stepwise by at least onefirst retard correction value SK₁, and ,during subsequent absence ofsignals indicative of said knock, K, said ignition angle α_(z) is resetin an advance direction stepwise by a first advance correction value RK₁toward said predetermined characteristic diagram reference level valueα_(v) ; and g) said microprocessor adaptively controls said knock, K, ona long term basis during transitions between said first operatingcondition having said first knock limit and a second operating conditionhaving a second knock limit: i) in response to said knock sensor sensingat least one knock, by resetting said predetermined characteristicdiagram reference level value α_(v) by an adaptation value L_(z) in adirection below said first knock limit, to a second predeterminedcharacteristic diagram reference level value α_(L).sbsb.Z such that saidshort-term knock control steps SK₁ are thereafter referred to saidsecond predetermined characteristic reference level diagram valueα_(L).sbsb.Z as a new reference level corresponding to an ignition pointat said second operating condition, to provide corresponding signals tosaid means for advancing or retarding said ignition angle signal; andii) in response to subsequent absence of signals indicative of saidknock sensor sensing a subsequent minimum number of knockless ignitions,by resetting said short-term knock control with a second retardcorrection value SK₂ and a second advance correction value RK₂, saidsecond retard and said second advance corrections values SK₂, RK₂ havingsmaller magnitudes of correction than said first retard and said firstadvance correction values, SK₁, RK₁, respectively, to providecorresponding signals to said means for advancing or retarding saidignition angle signal resulting in more efficient engine combustion. 2.A knock control system as in claim 26 which includes:a) means forcounting one or more knock signals K in a first repetitive monitoringtime interval t¹ _(B) ; and b) said means for advancing or retardingsaid ignition angle signal resetting said predetermined characteristicdiagram value α_(v) by said adaption value L_(z) in response to a signalfrom said counter representing a predetermined number of knock signalscounted in said interval.
 3. A knock control system as in claim 2wherein:a) said memory includes a correction characteristic diagramstored therein; b) said adaption value L_(z) is entered in saidcorrection characteristic diagram in said memory upon said engineleaving said second operating condition; c) said value L_(z) iswithdrawn from said memory as a learned correction magnitude value; andd) said predetermined characteristic diagram reference level value α_(v)is adapted by the amount of L_(z) as said second predeterminedcharacteristic diagram reference level value α_(LZ) when said secondoperating condition is reached again by said engine.
 4. A knock controlsystem as in claim 3 wherein:a) said adaption value L_(z) is reset insteps by a predetermined return magnitude value in the direction of saidpredetermined characteristic diagram reference level value α_(v) inresponse to said counter means signaling that a minimum threshold numberof knocks K has not been exceeded during said monitoring time intervalt¹ _(B).
 5. A knock control system as in claim 4 wherein:a) saidshort-term knock control with said second retard and said second advancecorrection values SK₂, RK₂ includes switching back to said short-termknock control with said first retard and first advance correction valuesSK₁, RK₁ in response to said counter means signaling at least oneinstance of knock K occurring within a second monitoring interval t²_(B) during a return through said second said second retard and saidsecond advance correction values SK₂, RK₂.
 6. A knock control system asin claim 5 wherein:a) said short-term knock control switch-back to saidfirst retard and first advance correction values SK₁, RK₁ is maintainedin response to said counter signaling the occurrence of repeatedinstances of knock K until correction has been worked through.
 7. Aknock control system as in claim 5 wherein:a) one of said first retardcorrection values SK₁ associated with said first operating condition isselected as said adaption value L_(z).
 8. A knock control system as inclaim 5 wherein:a) said adaption value L_(z) is an average of each ofsaid first retard correction values SK₁ in said first monitoring timeinterval t¹ _(B).
 9. A knock control system as in claim 5 wherein:a)said adaption value L_(z) is an average of each of said first retard andsaid first advance correction values SK₁, RK₁ in said first monitoringtime interval t¹ _(B).
 10. A knock control system as in claim 5wherein:a) said adaption value L_(z) is retained in said memory evenwhen the internal combustion engine is stopped, and is immediatelyavailable as an adaption magnitude upon restarting said engine.
 11. Aknock control system method as in claim 6 wherein:a) said adaption valueL_(z) is retained in said memory even when the internal combustionengine is stopped, and is immediately available as an adaption magnitudeupon restarting said engine.
 12. A knock control system as in claim 7wherein;a) said adaption value L_(z) is retained in said memory evenwhen the internal combustion engine is stopped, and is immediatelyavailable as an adaption magnitude upon restarting said engine.
 13. Aninternal combustion engine control system for suppression of knockevents, K, in an internal combustion engine, which system includes amemory containing data representing ignition advance and retard valuesgenerated by method of:a) providing to said memory a predeterminedcharacteristic diagram reference level value, α_(v), from a base diagramhaving a plurality of characteristic performance values, whichcharacteristic diagram value, α_(v), corresponds to a first referencelevel for an ignition point of the engine at a first operating conditionhaving a first knock limit; b) producing signals indicative of theoccurrence of a knock, K, in at least one cylinder of the engine; c)producing signals indicative of an ignition angle, α_(z), of saidcylinder of the engine; d) producing a signal representative of anadvance or retard of said ignition angle, α_(z) ; e) advancing orretarding said ignition signal on a short-term basis during said firstoperating condition upon comparison with a predetermined characteristicdiagram value α_(v) corresponding to a first reference level for theignition point at said first operating condition retrieved from saidbase diagram of a plurality of characteristic performance values storedin said memory, so that when said knock K occurs, said ignition angleα_(z) is reset in a retard direction stepwise by at least one firstretard correction value SK₁, and during subsequent absence of said knockK, said ignition angle α_(z) is reset in an advance direction stepwiseby a first advance correction value RK₁ toward said predeterminedcharacteristic diagram reference level value α_(v) ; f) adaptivelycontrolling said knock, K, on a long term basis during transitionsbetween said first operating condition having said first knock limit anda second operating condition having a second knock limit, by: i)resetting said predetermined characteristic diagram value α_(v) inresponse to a knock sensor sensing at least one knock by an adaptationvalue L_(z) in a direction below said first knock limit, to a secondpredetermined characteristic diagram value α_(L).sbsb.Z, such that saidshort-term knock control steps SK₁ are thereafter referred to saidsecond predetermined characteristic diagram value α_(L).sbsb.Z as a newreference level corresponding to an ignition point at said secondoperating condition; and ii) resetting said short-term knock control inresponse to a knock sensor sensing a subsequent minimum number ofknockless ignitions, with a second retard correction value SK₂ and asecond advance correction value RK₂, said second retard and said secondadvance correction values SK₂, RK₂ having smaller magnitudes ofcorrection than said first retard and said first advance correctionvalues, SK₁, RK₁, respectively.
 14. An internal combustion enginecontrol system as in claim 13 wherein said memory includes datarepresenting engine knock control parameters generated by the stepsof:a) determining a first monitoring time internal t¹ _(B) ; b)selecting a minimum threshold number of knocks, K, to occur within saidfirst monitoring time interval t¹ _(b) ; c ) determining a secondmonitoring time interval t² _(B) ; and d) selecting a number of knocks,K, to occur within said second monitoring time interval t² _(B).
 15. Aninternal combustion engine control system as in claim 14 wherein saidmemory data generating steps include accumulating repeated instances ofknock, K.
 16. An internal combustion engine control system as in claim14 wherein said memory data generating steps include selecting one ofsaid first retard correction values SK, is said adaption value L₂. 17.An internal combustion engine control system as in claim 14 wherein saidmemory data generating steps include determining said adaption valueL_(z) to be an average of each said first retard correction values SK₁in said first monitoring time interval t¹ _(B).
 18. An internalcombustion engine control system as in claim 14 wherein said memory datagenerating steps include determining said adaption value L_(v) to be anaverage of each of said first retard and said first advance correctionvalues SK₁, RK₁ in said first monitoring time interval t¹ _(B).